This investigation seeks to delineate the biochemical reactions involved in the inactivation and proteolytic degradation of a cell-associated fructosyltransferase (FTase) produced by Streptococcus salivarius. We continue to concentrate on the FT inactivation step because this reaction appears to 'mark' the enzyme for subsequent proteolysis FT when resting cell suspensions were incubated with low concentrations (0.5f MuM ) of copper ions, FT was inactivated in a time dependent manner. The activity of a cell-free preparation of the enzyme was unaffected by 5.0 cu++H. Inactivation of the cell-associated FT required the catabolism of endogenous intracellular polysaccharide or exogenously supplied glucose and was prevented by inhibitors of glycolysis (iodoacetate, NaF, and Na2HAs04). In starved permeablized cells, NADH could replace glucose whereas NADPH or ATP could not. The rate of FT inactivation under these conditions was markedly stimulated by 02 while several other enzymes (glutamate dehydrogenase, phosphofructokinase, aldolase) were completely stable. Aerobically grown cells had high levels of NADH oxidase and low levels of FT, while cells grown under microaerophilic conditions exhibited the reverse relationship. Results from oxygen radical scavenger studies implicated OH in the inactivation. OH is thought to be formed as follows: 1) FT-Cu++ + 02 leads to FT-Cu++ 02 2) FT-Cu+ + H202 leads to FT-Cu++ +OH+OH minus H202 and 02 appear to be products of the NADH oxidase system.